128 



MAGNETS AND ELECTRICITY 



field. If we use a cover of fresh blue print paper, and expose it to 

 light with the filings in place, the position of the filings will be printed on 

 the paper. 



139. The Earth a Magnet. The earth itself is a 

 great magnet, having its north and south poles. It is to 

 these magnetic poles, not to the geographical poles, that 



the compass needle 

 points. The north mag- 

 netic pole is now in 

 Northern Canada, inside 

 the Arctic Circle. It is 

 slowly moving westward. 



The latest determination 

 of the position of the north 

 magnetic pole was made by 

 Amundsen, the Norwegian 

 explorer, in 1905; he found 

 it to be in latitude 70 5' N., 

 and in longitude 96 46' W. 

 (Fig. 115). This is the same 

 Amundsen who discovered 

 the earth's south geographical 

 pole in 1912. 



20*| 



20 W 



FIG. 115. 



The North Magnetic Pole, the " Line of No Vari- 

 ation," and the "Declination" in Different 

 Parts of North America. 



Since the earth's north 

 magnetic pole is not the same as its north geographical 

 pole, a compass will point due north only at certain places. 

 The "line of no variation" is shown, for North America, 

 in Fig. 115. For all places east and west of this line the 

 compass shows a variation, or declination, from true north, 

 and the amount of variation must be known if the com- 

 pass is to be used accurately. In the eastern part of the 



